1. Field of the Invention
The invention relates to devices for detecting and obtaining information about an event.
2. Introduction to the Invention
A number of methods have been used (or proposed for use) to detect changes in variables, e.g. the presence of a liquid, the attainment of a predetermined temperature or pressure, the presence or absence of light or another form of electromagnetic radiation, or a change in the physical position of a movable member, e.g. a valve in a chemical process plant or a window in a building fitted with a burglar alarm system. Changes of this kind are referred to in this specification by the generic, term "event". Such detection methods are for example highly desirable to detect leaks from pipe lines, for example pipe lines carrying hydrocarbon liquids, leaks from steam lines into thermal insulation surrounding such lines, and leaks from tanks and pipes containing corrosive or noxious chemicals. U.S. Pat. No. 3,470,340 (Hakka) and U.K. Patent 1,355,176 (Nils Ostobo AB), for example, disclose devices for detecting the leakage of oil from oil pipelines. Each device comprises a material which swells when exposed to the leaking oil causing two metal contacts to touch and thereby trigger an alarm.